Default key matches the last 5 characters of the Network Name printed on a label on the device. ( or Last 5 of the MAC Address )
SSID Name matches the last 6 characters of the MAC Address.

Valid values for 64-bit RC4 encryption

5-digit case-sensitive Alphanumeric Value.
Example: SECU1

10-digit Hexadecimal Value in the range of “a-f”, “A-F” and “0-9”.
Example: ABCD1234FE

Valid values for 128-bit RC4 encryption.

13-digit case-sensitive Alphanumeric Value.
Example: SECURITY12345

26-digit Hexadecimal Value in the range of “a-f”, “A-F” and “0-9”.
Example: ABCDEF1234567890FEDCBA4321

Included ia a TXT files to help you decypher your keys.

Reloading RG-1000 in case you forget your password

If these values cannot be provided/retrieved, it is impossible for you to update the Encryption Key and the Network Name. You will not be able to use the Residential Gateway Setup Utility to change it as well.

IN THIS CASE YOU NEED TO SOFT RELOAD IT TAKES ABOUT 5 MINS

Here's how (remotely of course)
Soft Reloading

If you used the AP Manager, instead of the Residential Gateway Setup Utility, the Residential Gateway configuration will be checked for unexpected settings. When detected, the Residential Gateway Setup Utility will set these settings back to default

Therefore, you have to Perform a Soft Reload.

The AP Manager program is a tool for LAN administrators or system supervisors to configure and monitor the performance of:

Force Reloading AP/RG

A Forced Reload, which you can perform with the AP Manager, allows you to recover from a situation where the Base Station:

O has stopped responding to the system
O has been configured with an incorrect IP address or
Encryption Key, or you have forgotten the unique identifiers to
access the Base Station.
O You have mislaid the Access Control password, or you would
like to disable Access Control

Forced Reload Configuration

Encryption No encryption (off)
Access Point IP Address 153.69.254.254

[IP Address note]
In environments with DHCP or BOOTP services, this address will be assigned automatically when the MAC Address of the unit was added to the IP Configuration table of the DHCP/BOOTP server system